At present, LED lamps are fixed to the wall of a bathtub. In this way, the colorful light that they emit is used for decoration so that they could bring visual aesthetic feeling for humans bathing in the bathtub. For this purpose, the LED underwater lamp used in the bathtub is popular with customers. However, the structure of such product in the prior art is relatively simple, which comprises an LED lamp body, an LED bulb disposed inside the LED lamp body and a power line integrated with one end of the LED lamp body. During mounting, the LED lamp body is directly mounted into a hole in the wall of the bathtub through a retaining nut. In this way, the retaining nut has to be screwed off from an inner side of the bathtub when it is needed to replace the LED lamp body, and it is requested that the whole outer housing of the bathtub is open. Therefore, the replacement is relatively troublesome and time-consuming. Moreover, water-proof treatment needs to be carried out after the replacement, which further results in very low efficiency.